The invention is based on a fuel injection pump as generally defined hereinafter. A known rpm governor of this kind (used in Bosch distributor injection pump Type VE) has, in one version, only one leaf spring as an intermediate spring, which has the function of a so-called starting spring generating an increased fuel quantity for starting; another version has a combination of this starting spring with a helical spring which governs the idling rpm. While the starting spring is as soft as possible and has the sole function of displacing the second lever and thus the injection quantity control member, in the starting position, into a position for an increased starting quantity which is greater than the maximum full-load injection quantity, the idling spring has the task, in the idling position of the governor, of keeping the second lever and thus the injection quantity control member, each acting as a counterforce to the rpm signal transducer which at idling rpm can generate only small forces, in a position that corresponds to a balance of forces (springs, rpm signal transducer).
Only when the idling rpm is exceeded, is the idling spring also compressed, so that in the upper idling rpm range the two levers rest positively on one another. The idling spring, however, is compressed via the first lever even at idling rpm and with sufficient load, to the extent that a stop determining the initial position of the first lever permits this to happen.
Naturally, a single helical or leaf spring acting as a starting and idling spring can also serve as the intermediate spring, if it is provided with a first, soft portion, for generating an increased starting quantity, and a second portion that is somewhat stiffer, for governing the idling rpm.
In a Diesel engine, the actual consumption per engine cylinder is known to vary, in contrast to the injection quantity metered per engine cylinder by the injection pump, which is identical for all the engine cylinders at a particular position of the rpm governor. The variation in the quantity usable by the engine cylinders may, during idling, amount to 30% of the average injection quantity and so is particularly disadvantageous at that time. For instance, if the average idling quantity is 5 mm.sup.3, the variation may certainly amount to 2 mm.sup.3. These variations, considered in dynamic terms, have a corresponding, albeit very brief, effect on the rpm of the engine, and via the rpm signal transducer of the rpm governor, on the injection quantity in turn; depending on which engine cylinder is affected by these variations, they also cause a possibly undesirable amplification or retarding of the mean idling rpm that is to be governed. For this reason, the speed droop (P-degree) should be as great as possible, which would necessitate the stiffest possible idling springs. In order to be able to travel a predetermined distance (governor path) toward a stiff spring, a relatively large variation in force is necessary, in contrast to a soft spring. As a result of the variations in the brakings and surges arising during combustion in the engine, corresponding surges of force are exerted by the rpm signal transducer onto the second lever, which can be absorbed by a stiff spring in such a way that jerking or engine jolting during idling is prevented.
However, as noted above, a stiff idling spring has a high P degree, which during idling can amount to 40%. At idling rpm levels of 600 rpm, this already accounts for 240 rpm. This high P degree causes unstable engine operation, known as "seesawing" This seesawing can be counteracted in turn by a soft spring with a correspondingly low P degree, that is, a spring in which, even at relatively small changes in force of the rpm signal transducer, long travel paths (governor paths) are already traversed. Because of the low P degree of soft springs, addition and subtraction of the slight changes in fuel quantity effected by the deviation and affecting the rpm are substantially absorbed, so that although a low P degree is attained (little seesawing, substantially constant rpm), jerking or jolting of the engine is still possible. In known rpm governors a relatively high P degree is accordingly taken into consideration so as to avoid unpleasant jerking, especially in Diesel engines for passenger cars.
In known rpm governors of the type initially described above, there is accordingly an attempt, by means of the selected stiffness of the idling spring, to strike a compromise between the least possible engine jolting and little seesawing of the engine, yet without having to increase the idling rpm.
This problem exists not only with an idling spring as the intermediate spring; it applies equally to governors of injection pumps for stationary engines or other operations needing to be governed, in which the rpm must be maintained at a constant level. Here again there is a need to avoid both seesawing on the one hand, that is, a deviation from the constant rpm, and on the other hand engine jolting, which could cause damage to the aggregate unit driven by the engine.